International Space Station’s cooling system fails, but the crew is safe for now

One of the International Space Station’s cooling systems has failed. Fortunately, there is a redundant cooling system, otherwise the six-person crew would be quickly bailing out and heading back to Earth aboard a Soyuz capsule before being cooked alive. NASA is now working out how to fix the primary cooling loop, to get the space station back to full working order. The situation is being described by NASA as “urgent” but not “life-threatening.”

The International Space Station, with an acre of solar panels, generates between 75 and 90 kilowatts of power. This power is used by the ISS’s systems, from life support, to storage freezers, to various lab experiments that are dotted throughout the interior. As you can imagine, consuming 80ish kilowatts of power generates a lot of waste heat — heat that has to be vented into space. To do this, the ISS has a cooling system — essentially a pump, a radiator, and some pipes filled with ammonia — that ferries heat from inside to outside, where the chills of outer space (-270 Celsius or -454 Fahrenheit) quickly dispose of the heat.

Looking down at Earth from the ISS’s cupola

There are two cooling loops — Loop-A and Loop-B — and for some reason Loop-A failed late on Wednesday. Usually both systems work in concert to keep the ISS and its various systems cooled, but now Loop-B must bear all of the load. To compensate, some non-critical systems and science experiments (the Japanese Kibo lab, the European Columbus lab) have been disabled. Life support, storage freezers, and other systems that are of vital importance are still up and running.

NASA is currently working out exactly what’s wrong with Loop-A, and how to fix it. So far, it sounds like a flow control valve malfunctioned, causing an anomalous temperature imbalance, which triggered an automatic shutdown when the system reached a preset threshold temperature. The fix might be as simple as uploading some new management software for the valve, or it may require a spacewalk. (See: A mysterious lightning sprite, photographed from the International Space Station.)

The International Space Station, with Endeavor Space Shuttle docked (the penultimate flight of the Shuttle)

A cooling system failure, along with thirteen other issues with the ISS that NASA prepares for, are referred to by NASA as the “Big 14.” The Big 14 specifically refers to the ISS’s electrical and cooling systems, and excludes life-support systems (which have more levels of redundancy and are managed differently). NASA allots a two-week period to prepare for the repair of a Big 14 issue, but if a spacewalk is already scheduled (as was the case when a cooling pump failed in July 2010) the fix can be carried out a lot sooner.

Hopefully, everything will go to plan and the astronauts and cosmonauts aboard the ISS will fix Loop-A in short order. The worst-case scenario is that Loop-B fails before they can fix Loop-A — but even then, we’re not talking about Apollo 13-levels of drama. Given the sheer size of the ISS, there would be enough good air in the system for a few days of repair works — and if a fix couldn’t be found, there are always enough Soyuz capsules attached to the ISS to ensure that everyone on board has a ride back to Earth.

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